<!DOCTYPE html>
<html>
 <body>
   <div id="source" style="width: 3ch"></div>
   <div id="target" style="width: 0">
    This is a test
   </div>
   <script>
    document.getElementById("target").style.lineHeight =
      document.defaultView
              .getComputedStyle(document.getElementById("source"), "").width;
   </script>
 </body>
</html>
